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These Grade 12 Animal Nutrition notes follow the South African CAPS Agricultural Sciences curriculum. Animal Nutrition is assessed in Agricultural Sciences Paper 1 and includes feed components, digestion, feed classification, digestibility, protein quality, energy values, nutritive ratio and ration formulation.
The notes use farm-animal examples such as cattle, sheep, goats, pigs and poultry. They are useful for examination revision, but are not a substitute for species-specific feeding advice from a veterinarian or animal nutritionist.
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1. Meaning and importance of animal nutrition
Animal nutrition is the study of how animals obtain, digest, absorb and use nutrients from feed.
A balanced ration supplies nutrients an animal needs for:
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- Maintenance of normal body functions
- Growth and tissue repair
- Reproduction
- Work and movement
- Production of milk, meat, wool or eggs
- Regulation of body temperature
A ration deficient in energy, protein, minerals or vitamins may result in slow growth, poor reproduction, disease, low production or death.
2. Digestive systems
Ruminants
Cattle, sheep and goats are ruminants. Their stomach has four compartments:
| Compartment | Main functions |
|---|---|
| Rumen | The largest compartment. It stores and mixes feed and contains microorganisms that digest cellulose. Volatile fatty acids are absorbed through the rumen wall and papillae. |
| Reticulum | Works with the rumen as the reticulorumen, traps foreign objects and helps form the bolus regurgitated during rumination. |
| Omasum | Its folds increase surface area. It absorbs water and some volatile fatty acids and helps reduce feed particle size. |
| Abomasum | The true or glandular stomach. It secretes hydrochloric acid and digestive enzymes. |
The rumen normally has little or no oxygen, adequate moisture and regular feed intake. Its temperature is approximately 38–42 °C and its pH approximately 5.5–6.5, according to the 2024 NSC Agricultural Sciences Paper 1 memorandum.
Examination reminder: the abomasum, not the rumen, is the true stomach.
Non-ruminants
A pig is an example of a non-ruminant. It has a single stomach. Digestion depends mainly on mechanical breakdown and enzymes released in the mouth, stomach and small intestine. The pancreas and liver also provide important digestive secretions.
Fowl
The important parts of a bird’s digestive system are:
| Structure | Function |
|---|---|
| Crop | Temporarily stores and softens feed. |
| Proventriculus | The glandular stomach; secretes digestive juices. |
| Ventriculus or gizzard | The muscular stomach; grinds feed, often with grit. |
| Small intestine | Completes much of digestion and absorbs nutrients. |
| Caeca | Allow some fermentation and absorption of fermentation products. |
| Cloaca | A common chamber for the digestive, urinary and reproductive tracts. |
Do not confuse the proventriculus and gizzard: the proventriculus is glandular, while the gizzard is muscular and performs grinding.
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Ruminants initially swallow feed after limited chewing. Feed enters the rumen and reticulum, where microorganisms ferment plant material. The animal then performs rumination:
- Partly digested feed is regurgitated.
- The feed is chewed again.
- It is mixed with saliva.
- It is swallowed a second time.
Rumen microorganisms:
- Digest cellulose and hemicellulose
- Help break down proteins
- Produce volatile fatty acids
- Synthesise some amino acids
- Synthesise certain vitamins
The microorganisms later pass into the abomasum and small intestine, where they are digested and become a source of nutrients themselves. The 2024 NSC Agricultural Sciences Paper 1 memorandum identifies cellulose digestion, protein breakdown, amino-acid synthesis and vitamin synthesis among their functions.
4. Digestion in non-ruminants and fowl
Mouth
Feed is mechanically broken down and moistened with saliva. Enzymatic digestion may begin in the mouth.
Stomach
The stomach mixes feed and provides an acidic environment through hydrochloric acid. Protein digestion begins here.
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Small intestine
Most enzymatic digestion and absorption occur in the small intestine.
- Bile from the liver emulsifies fats, helping lipase act more effectively.
- Pancreatic enzymes digest carbohydrates, proteins and fats.
- Intestinal glands add further digestive secretions.
- Villi and microvilli provide a large surface area for absorption.
Bile also helps neutralise acidic chyme, assists absorption of fatty acids, glycerol and fat-soluble vitamins, and reduces putrefaction. These functions are listed in the 2024 NSC Agricultural Sciences Paper 1 memorandum.
Large intestine
The large intestine absorbs water, supports some microbial activity, and forms and stores faeces.
5. Components of feed
Water
Water is an essential feed component, not merely a drink. It:
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- Removes waste products
- Regulates body temperature
- Lubricates feed
- Supports chemical reactions
- Assists mechanical digestion
- Supports milk production
The 2023 NSC Agricultural Sciences Paper 1 memorandum lists these functions as acceptable answers.
Proteins
Proteins are made from amino acids. They are required for:
- Growth and repair of body tissue
- Muscle, skin, hair, wool and feather formation
- Enzyme and hormone production
- Reproduction and production
- Antibody formation
Essential amino acids must be supplied in the feed because the animal cannot produce enough of them.
Carbohydrates
Sugars, starch and crude fibre are carbohydrates. They provide energy. Sugars and starch are generally digested more readily than crude fibre. Ruminants can use cellulose more effectively because rumen microorganisms break it down.
Fats and oils
Fats and oils:
- Supply concentrated energy
- Provide essential fatty acids
- Improve palatability
- Assist absorption of vitamins A, D, E and K
- Provide insulation and protection
Minerals
Minerals are divided into macro-elements and trace elements.
| Macro-elements | Trace elements |
|---|---|
| Calcium, phosphorus, magnesium, sodium, chlorine, potassium and sulphur | Iron, iodine, zinc, selenium, copper and cobalt |
Mineral deficiencies can cause poor growth, weak bones, anaemia, abnormal skin or hair, poor reproduction, reduced production and specific deficiency diseases. CAPS requires learners to study functions and deficiencies of the listed minerals.
Vitamins
The curriculum includes the following vitamins:
| Water-soluble vitamins | Fat-soluble vitamins |
|---|---|
| B1, B2, B6 and B12 | A, D, E and K |
Fat-soluble vitamins are absorbed with dietary fat and may accumulate in the body. CAPS requires their functions and two deficiency symptoms for the listed vitamins.
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6. Feed classification
Roughages
Roughages generally contain more crude fibre and provide bulk. Examples include hay, grass, lucerne, straw and silage. They are particularly important in ruminant feeding.
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Concentrates
Concentrates generally contain less crude fibre and more digestible nutrients. They include:
- Energy-rich concentrates: maize meal, oats and other cereal products
- Protein-rich concentrates: oilcake meals and other high-protein feeds
Classify a feed according to its nutrient analysis, especially crude-fibre content, rather than relying only on its common name. The 2025 NSC Agricultural Sciences Paper 1 marking guideline classified wheat bran as more digestible than grass hay because it contained less crude fibre.
Supplements and rations
Supplements correct a deficiency or improve a ration. Examples include mineral licks, salt, protein supplements, vitamin supplements, non-protein nitrogen and molasses.
A maintenance ration supplies nutrients for normal body functions. A production ration is additional feed supplied above maintenance to support work or production.
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Digestibility is the proportion of feed an animal can digest and absorb. The digestibility coefficient is calculated using dry matter:
Digestibility coefficient (%) = [(dry matter intake − dry matter in manure) ÷ dry matter intake] × 100
Worked example
An animal consumes 30 kg of feed containing 8% water. The manure contains 12 kg of dry matter.
- Calculate water in the feed: 0.08 × 30 = 2.4 kg.
- Calculate dry matter intake: 30 − 2.4 = 27.6 kg.
- Subtract dry matter in manure: 27.6 − 12 = 15.6 kg.
- Calculate the coefficient: (15.6 ÷ 27.6) × 100 = 56.5%.
The digestibility coefficient is therefore 56.5%. The official NSC formula uses dry matter intake and dry matter in manure, not wet feed mass.
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- Crude-fibre content
- Age and maturity of the plant
- Type of animal
- Amount of feed consumed
- Grinding, milling or crushing
- Pelleting
- Cooking, heating or steaming
- Soaking
- Chemical treatment
- Mixing complementary feeds
- Time available for digestion
The 2015 NSC Agricultural Sciences Paper 1 memorandum accepts processing, pelleting, heating, soaking and mixing complementary feeds among methods that can improve digestibility.
8. Biological value of protein
Biological value (BV) is an index of protein quality. A protein with a high biological value:
- Contains a suitable balance of essential amino acids
- Is readily digested
- Is efficiently used for tissue growth and repair
Egg and milk are commonly used examples of high-biological-value proteins in the CAPS content. An ideal protein supplies essential amino acids in proportions that closely match the animal’s requirements.
9. Energy value of feed
Energy is progressively lost as feed passes through the animal:
| Energy value | Meaning |
|---|---|
| Gross energy (GE) | Total energy released when feed is completely oxidised. |
| Digestible energy (DE) | GE minus energy lost in faeces. |
| Metabolic energy (ME) | DE minus energy lost in urine and gases such as methane. |
| Net energy (NE) | ME minus heat loss. Available for maintenance, growth, reproduction, work and production. |
The formulas are:
- DE = GE − energy lost in faeces
- ME = DE − energy lost in urine and gases
- NE = ME − heat loss
Do not calculate metabolic energy by subtracting only urine loss from gross energy. Faecal energy must first be removed, and gaseous losses must also be considered. These energy values and calculations are included in the CAPS curriculum.
10. Nutritive ratio
The nutritive ratio (NR) compares digestible protein with digestible non-nitrogenous nutrients. It is normally written with the protein portion as 1:
NR = 1 : digestible non-nitrogenous nutrients ÷ digestible protein
The non-nitrogenous portion includes digestible carbohydrates and the energy equivalent of digestible fat.
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- A narrow ratio indicates relatively more digestible protein.
- A wide ratio indicates relatively more carbohydrates and fats.
A ratio of 1:4 means that for every one part of digestible protein, there are four parts of digestible non-nitrogenous nutrients. It does not mean four parts of protein for every one part of carbohydrate.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.11. Pearson square method
The Pearson square balances two feeds to achieve a desired percentage of one nutrient, commonly crude protein. It does not automatically balance the complete ration.
Worked example
Feed A contains 9% protein, Feed B contains 44% protein, and the target mixture contains 17% protein.
| Feed | Protein | Parts in mixture |
|---|---|---|
| Feed A | 9% | 44 − 17 = 27 |
| Feed B | 44% | 17 − 9 = 8 |
| Target | 17% | Total = 35 parts |
- Subtract the target from the higher percentage: 44 − 17 = 27 parts of Feed A.
- Subtract the lower percentage from the target: 17 − 9 = 8 parts of Feed B.
- Add the parts: 27 + 8 = 35.
- Calculate Feed A: 27 ÷ 35 × 100 = 77.14%.
- Calculate Feed B: 8 ÷ 35 × 100 = 22.86%.
The mixture should contain approximately 77.14% Feed A and 22.86% Feed B. The 2023 NSC Agricultural Sciences Paper 1 memorandum includes Pearson-square feed-mixing calculations.
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The Pearson square balances only the selected nutrient. Energy, fibre, minerals, vitamins and amino acids must still be evaluated separately.
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12. Examination focus and current status
Animal Nutrition is assessed in Agricultural Sciences Paper 1 under the South African NSC structure, according to the Department of Basic Education Grade 12 Agricultural Sciences Examination Guidelines. The Department’s examination page lists 2025 November Agricultural Sciences papers and memoranda for access in 2026.
Recent official examination material tests ruminant stomach compartments, rumen microorganisms, bile, feed classification, Pearson-square calculations, digestibility coefficients and energy values. For examples, see the Department of Basic Education’s 2024 NSC Agricultural Sciences Paper 1 memorandum and 2023 NSC Agricultural Sciences Paper 1 memorandum.
Practise both definitions and calculations: marks can be lost through using wet mass, reversing Pearson-square differences or giving an incomplete function.
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| Incorrect statement | Correct version |
|---|---|
| The rumen is the true stomach. | The abomasum is the true or glandular stomach. |
| The gizzard is the glandular stomach of a fowl. | The proventriculus is glandular; the gizzard is muscular and grinds feed. |
| Digestibility uses wet feed mass. | Use dry matter intake and dry matter in manure. |
| A wide nutritive ratio means high protein. | A wide ratio means more digestible non-nitrogenous nutrients relative to protein. |
| The Pearson square balances the entire ration. | It balances one selected nutrient between two feeds. |
| Rumen microorganisms only digest cellulose. | They also help break down protein and synthesise amino acids and vitamins. |
FAQ
What is animal nutrition?
Animal nutrition is the study of how animals obtain, digest, absorb and use nutrients from feed.
Which compartment is the true stomach of a ruminant?
The abomasum is the true or glandular stomach. The rumen, reticulum and omasum have different storage, fermentation and absorption functions.
What is the difference between the proventriculus and gizzard?
The proventriculus is the glandular stomach of a fowl and secretes digestive juices. The gizzard is the muscular stomach that grinds feed.
Why is dry matter used when calculating digestibility?
The Grade 12 formula uses dry matter intake and dry matter in manure rather than wet feed mass, so the calculation is based on the feed’s dry matter.
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It calculates the proportions of two feeds needed to reach a target percentage of one selected nutrient, usually crude protein. It does not balance every nutrient in the ration.
What is a production ration?
A production ration is feed supplied above maintenance to support work or production such as milk, meat, wool or eggs.
The Bottom Line
For Grade 12 Animal Nutrition, master the distinctions that appear in examinations: the abomasum is the true stomach, the proventriculus is the glandular stomach of a fowl, digestibility uses dry matter, and Pearson square balances only one selected nutrient. Then practise the digestibility, energy and ration calculations until each step is clear.
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